Visual Studio Ultimate can use a computer or a group of computers to generate simulated load for testing, and to run tests remotely and concurrently on several computers. This group of computers consists of a single test controller and one or more test agents. You can use the test controller and test agent to generate more load than a single computer can generate alone or just test remotely.

The client is used to develop tests, run tests, and view test results.

The test controller is used to administer the test agents and collect test results.

The test agents are used to run the tests, and collect data including system information and ASP.NET profiling data defined in the test setting.

This architecture provides the following benefits:

The ability to scale out load generation by adding additional test agents to a test controller.

Flexibility for installing the client, test controller, and test agent software on the same or different computers. For example:

Local configuration:

Machine1: Visual Studio, controller, agent.

Typical remote configuration:

Machine1 and 2: Visual Studio (multiple testers can use the same controller).

Machine3: Controller (can have agents installed, too).

Machine4-n: Agent or agents all associated with the controller on Machine2.

Even though a test controller typically manages several test agents, an agent can only be associated with a single controller. Each test agent can be shared by a team of developers. This architecture makes it easy to increase the number of test agents, thereby generating larger loads.

The test controller manages a set of test agents to run tests. The test controller communicates with test agents to start tests, stop tests, track test agent status, and collect test results.

Test Controller

The test controller provides a general architecture for running tests, and includes special features for running load tests. The test controller sends the load test to all test agents and waits until all the test agents have initialized the test. When all test agents are ready, the test controller sends a message to the test agents to start the test.

Test Agent

The test agent runs as a service that listens for requests from the test controller to start a new test. When a request is received, the test agent service starts a process on which to run the tests. Each test agent runs the same load test.

Test agents are assigned a weight by the administrator, and load is distributed according to a test agent’s weighting. For example, if test agent 1 has a weighting of 30, and test agent 2 has a weighting of 70, and the load is set to 1000 users, then test agent 1 simulates 300 virtual users whereas test agent 2 simulates 700 virtual users. For more information, see Managing Test Controllers and Test Agents.

The test agent takes as input a set of tests and a set of simulation parameters. A key concept in Visual Studio Ultimate is that tests are independent of the computer on which they are run.

Caution

Installing a test agent on a machine that is part of a Network Load Balancer setup is not supported.

The following illustration shows the connection points between the test controller, the test agent, and the client. It outlines which ports are used for incoming and outgoing connections as well as security restrictions used on these ports.

Visual Studio Load Test Virtual User Pack 2010 licenses use multiprocessor architecture, which allows the machine on which they are installed to use more than one processor.

The number of virtual users who are allowed on a local test run or remotely are as follows:

Local load test run without Visual Studio Load Test Virtual User Pack 2010 installed: If you use Visual Studio Ultimate without a Visual Studio Load Test Virtual User Pack 2010 installed on your local machine, you are limited to 250 users. The local machine is also limited to one core on the client CPU.

If your load test starts with more than 250 virtual users, or increases the virtual user count during the load test beyond 250 users, it will stop with an error that indicates a license violation.

Local load test run with a Visual Studio Load Test Virtual User Pack 2010 installed: If you use Visual Studio Ultimate with a Visual Studio Load Test Virtual User Pack 2010 installed on your local machine, you can run a load test that uses up to the maximum number of virtual users for whom you have purchased licensing.

Note

If you use more virtual users than your license limit, it will not stop the run, but it will add an error into the load test results and into the Application event log on the machine.

Adding a Visual Studio Load Test Virtual User Pack 2010 in a nontest controller scenario has the added benefit of unlocking all machine processors for use. Without a Visual Studio Load Test Virtual User Pack 2010, your local machine can use only the first processor. After you have added a Visual Studio Load Test Virtual User Pack 2010, load tests can use all processors on the machine when they run.

Remote load test run with Visual Studio Load Test Virtual User Pack 2010 installed by using a controller and agents: If you use Visual Studio Ultimate and have a test controller and one or more test agents installed with the required Visual Studio Load Test Virtual User Pack 2010, you can perform remote load test runs with the maximum number of virtual users for whom you have purchased licensing.

Load test that uses one remote machine

Load test that uses several remote machines

Note

If you specify more virtual users than your license limit, it will not stop your run, but it will add an error into the load test results and into the machine's Application event log.

Visual Studio Load Test Virtual User Pack 2010 License keys are applied per machine. Therefore, if you have both Visual Studio Ultimate installed using more than 250 users and a test controller installed on the same machine, you must enter the license key only one time on that machine to enable the use of the virtual users in both tools.

To enable the newly added license key or keys to be recognized, you must restart the test controller service or Visual Studio Ultimate, depending on the tool that you used.